1. Field of the Invention
The present invention generally relates to a chemically amplified resist composition, and more particularly, the present invention relates to a resist composition comprising a photosensitive polymer having lactone in its backbone.
2. Description of the Related Art
As the integration density and complexity of semiconductor devices continue to increase, the ability to form ultra-fine patterns becomes more and more critical. For example, in 1-Gigabit or higher semiconductor devices, a pattern size having a design rule of 0.2 xcexcm or less is needed. For this reason, in lithography processes, the lower wavelength ArF eximer laser (193 nm) has emerged as a preferred exposure light source to the more conventional and higher wavelength KrF eximer laser (248 nm).
However, compared with conventional (KrF) resist materials, resist materials which are suitable for use with the ArF eximer laser suffer from a variety drawbacks. The most serious problems relate transmittance and resistance to dry etching.
Almost all well-known ArF resist compositions contain (meth)acryl-based polymers. Among these polymers, a methacrylate copolymer having an alicyclic protecting group, which is expressed by the formula below, has been suggested (J. Photopolym. Sci. Technol., 9(3), pp. 509 (1996)) 
This polymer has an adamantyl group, which contributes to enhancing resistance to dry etching, and a lactone group, which improves adhesiveness, in its methacrylate backbone. As a result, the resolution of the resist and the depth of focus are improved. However, resistance to dry etching is still weak, and serious line edge roughness is observed after line patterns are formed from the resist layer.
Another drawback of the aforementioned polymer is that the raw material used to synthesize the polymer is expensive. In particular, the manufacturing cost of a polymer having a lactone group, which is introduced to improve adhesiveness, is so high that its practical use as a resist is difficult.
As another conventional resist composition, a cycloolefin-maleic anhydride (COMA) alternating polymer having the following formula has been suggested (J. Photopolym. Sci. Technol., Vol. 12(4), pp. 553 (1999), and U.S. Pat. No. 5,843,624) 
In the production of a copolymer, such as a COMA alternating polymer having the formula above, the production cost of raw material is relatively inexpensive, but the yield of the polymer sharply decreases. In addition, the transmittance of the polymer is very low at a short wavelength region, for example at 193 nm. The synthetic polymers have in their backbone the alicyclic group, which exhibits prominent hydrophobicity, and thus the adhesiveness to neighboring material layers is very poor.
The copolymer has a glass transition temperature of 200xc2x0 C. or more due to the structural characteristic of the backbone. As a result, it is difficult to carry out an annealing process for eliminating free volume from the resist layer formed of the polymer, and accordingly the resist layer is influenced by ambient conditions which can cause, for example, a T-top profile of corresponding resist patterns. In addition, the resist layer itself becomes less resistant to ambient conditions during post-exposure delay, so that many problems can occur during subsequent processes with respect to the photoresist layer.
To improve the resolution of the resist layer, the polymer system must be charged with a polar group. In recent years, a technique of introducing a lactone group into a methacrylate monomer having an alicyclic protecting group, using the following alicyclic compounds with a lactone group, has been suggested so as to enhance the resistance to dry etching (J. Photopolym. Sci. Technol., Vol. 13(4), pp. 601 (2000), and Japanese Patent Laid-open No. hei 12-26446): 
Unfortunately, the yield of the monomer having the above formula is so low as to substantially increase manufacturing costs.
It is an objective of the present invention to provide a resist composition that can be produced at relatively low costs while exhibiting improved dry etching resistance, improved adhesiveness to underlying material layers, improved line edge roughness of line patterns, and improved contrast characteristics.
To achieve the objective of the present invention, there is provided a resist composition comprising a photosensitive polymer polymerized with (a) at least one of the monomers having the respective formulae: 
where R1 and R2 are independently a hydrogen atom, alkyl, hydroxyalkyl, alkyloxy, carbonyl or ester, and x and y are independently integers from 1 to 6, and (b) at least one comonomer selected from the group consisting of (meth)acrylate monomer, methacrylate monomer, maleic anhydride monomer, and norbornene monomer; and a photoacid generator (PAG).
In one embodiment of the resist composition, the comonomer may be maleic anhydride monomer, and the formula of the photosensitive polymer may be one selected from the formulae: 
where m/(m+q) is in the range of 0.01-0.5, 
where n/(n+q) is in the range of 0.01-0.5, and 
where (m+n)/(m+n+q) is in the range of 0.01-0.5.
In another embodiment of the resist composition, the comonomer may include a (meth)acrylate monomer and a maleic anhydride monomer, and the formula of the photosensitive polymer may be selected from the formulae: 
where R3 is a hydrogen atom or methyl, R4 is an acid-liable group, and m/(m+p+q) is in the range of 0.01-0.5, p/(m+p+q) is in the range of 0.1-0.6, and q(m+p+q) is in the range of 0.1-0.6, 
where R3 is a hydrogen atom or methyl, R4 is an acid-liable group, and n/(n+p+q) is in the range of 0.01-0.5, p/(n+p+q) is in the range of 0.1-0.6, and q(n+p+q) is in the range of 0.1-0.6, and 
where R3 is a hydrogen atom or methyl, R4 is an acid-liable group, and (m+n)/(m+n+p+q) is in the range of 0.01-0.5, p/(m+n+p+q) is in the range of 0.1-06, and q(m+n+p+q) is in the range of 0.1-0.6.
It is preferable that R4 is t-butyl, tetrahydropyranyl, or substituted or unsubstituted alicyclic hydrocarbon having from 6 to 20 carbon atoms. More preferably, R4 is 2-methyl-2-norbornyl, 2-ethyl-2-norbornyl, 2-methyl-2-isobornyl, 2-ethyl-2-isobornyl, 8-methyl-8-tricyclo[5.2.1.02,6]decanyl, 8-ethyl-8-tricyclo[5.2.1.02,6]decanyl, 2-methyl-2-adamantyl, 2-ethyl-2-adamantyl, 1-adamantyl-1-methylethyl, 2-methyl-2-fenchyl or 2-ethyl-2-fenchyl.
In another embodiment of the resist composition, the comonomer may include (meth)acrylate monomer, maleic anhydride monomer and norbornene monomer, and the formula of the photosensitive polymer may be one selected from the formulae: 
where R3 is a hydrogen atom or methyl; R4 is an acid-liable group; R5 and R6 are independently a hydrogen atom, hydroxyl, hydroxymethyl, 2-hydroxyethyloxycarbonyl, carboxyl, t-butoxycarbonyl, methoxycarbonyl, or substituted or unsubstituted alicyclic hydrocarbon having from 6 to 20 carbon atoms; m/(m+p+q+r) is in the range of 0.01-0.5; p/(m+p+q+r) is in the range of 0.1-0.6; q/(m+p+q+r) is in the range of 0.1-0.6; and r/(m+p+q+r) is in the range of 0.1-0.3, 
where R3 is a hydrogen atom or methyl; R4 is an acid-liable group; R5 and R6 are independently a hydrogen atom, hydroxyl, hydroxymethyl, 2-hydroxyethyloxycarbonyl, carboxyl, t-butoxycarbonyl, methoxycarbonyl, or substituted or unsubstituted alicyclic hydrocarbon having from 6 to 20 carbon atoms; n/(n+p+q+r) is in the range of 0.01-0.5; p/(n+p+q+r) is in the range of 0.1-0.6; q/(n+p+q+r) is in the range of 0.1-0.6; and r/(n+p+q+r) is in the range of 0.1-0.3, and 
where R3 is a hydrogen atom or methyl; R4 is an acid-liable group; R5 and R6 are independently a hydrogen atom, hydroxyl, hydroxymethyl, 2-hydroxyethyloxycarbonyl, carboxyl, t-butoxycarbonyl, methoxycarbonyl, or substituted or unsubstituted alicyclic hydrocarbon having from 6 to 20 carbon atoms; (m+n)/(m+n+p+q+r) is in the range of 0.01-0.5; p/(m+n+p+q+r) is in the range of 0.1-0.6; q/(m+n+p+q+r) is in the range of 0.1-0.6; and r/(m+n+p+q+r) is in the range of 0.1-0.3.
In another embodiment, the present invention provides a resist composition comprising a photosensitive polymer polymerized with (a) at least one of the monomers having the respective formulae: 
where v and w are independently integers from 1 to 6, and (b) at least one comonomer selected from the group consisting of a acrylate monomer, methacrylate monomer, maleic anhydride monomer, and norbornene monomer; and a photoacid generator (PAG).
In one embodiment of the resist composition above, the comonomer may be maleic anhydride monomer, and the formula of the photosensitive polymer may be one selected from the formulae: 
where k/(k+q) is in the range of 0.01-0.5, 
where l/(l+q) is in the range of 0.01-0.5, and 
where (k+l/(k+l+q) is in the range of 0.01-0.5.
In another embodiment of the resist composition, the comonomer may include a (meth)acrylate monomer, and the formula of the photosensitive polymer may be selected from the formulae: 
where R3 is a hydrogen atom or methyl, R4 is an acid-liable group, and k/(k+p) is in the range of 0.3-0.8, 
where R3 is a hydrogen atom or methyl, R4 is an acid-liable group, and l/(l+p) is in the range of 0.3-0.8, and 
where R3 is a hydrogen atom or methyl, R4 is an acid-liable group, and (k+l)/(k+l+p) is in the range of 0.3-0.8.
In another embodiment of the resist composition, the comonomer may include a (meth)acrylate monomer and maleic anhydride monomer, and the formula of the photosensitive polymer may be one selected from the formulae: 
where R3 is a hydrogen atom or methyl; R4 is an acid-liable group; k/(k+p+q) is in the range of 0.01-0.5; p/(k+p+q) is in the range of 0.1-0.6; and q/(k+p+q) is in the range of 0.1-0.6, 
where R3 is a hydrogen atom or methyl; R4 is an acid-liable group; l/(l+p+q) is in the range of 0.01-0.5; p/(l+p+q) is in the range of 0.1-0.6; and q/(l+p+q) is in the range of 0.1-0.6, and 
where R3 is a hydrogen atom or methyl; R4 is an acid-liable group; (k+l)/(k+l+p+q) is in the range of 0.01-0.5; p/(k+l+p+q) is in the range of 0.1-0.6; and q/(k+l+p+q) is in the range of 0.1-0.6.
In another embodiment of the resist composition, the comonomer may include a maleic anhydride monomer and norbornene monomer, and the formula of the photosensitive polymer may be one selected from the formulae: 
where R5 and R6 are independently a hydrogen atom, hydroxyl, hydroxymethyl, 2-hydroxyethyloxycarbonyl, carboxyl, t-butoxycarbonyl, methoxycarbonyl, or substituted or unsubstituted alicyclic hydrocarbon having from 6 to 20 carbon atoms; k/(k+q+r) is in the range of 0.01-0.5; q/(k+q+r) is in the range of 0.1-0.6; and r/(k+q+r) is in the range of 0.1-0.3, 
where R5 and R6 are independently a hydrogen atom, hydroxyl, hydroxymethyl, 2-hydroxyethyloxycarbonyl, carboxyl, t-butoxycarbonyl, methoxycarbonyl, or substituted or unsubstituted alicyclic hydrocarbon having from 6 to 20 carbon atoms; l/(l+q+r) is in the range of 0.01-0.5; q/(l+q+r) is in the range of 0.1-0.6; and r/(l+q+r) is in the range of 0.1-0.3, and 
where R5 and R6 are independently a hydrogen atom, hydroxyl, hydroxymethyl, 2-hydroxyethyloxycarbonyl, carboxyl, t-butoxycarbonyl, methoxycarbonyl, or substituted or unsubstituted alicyclic hydrocarbon having from 6 to 20 carbon atoms; (k+l)/(k+l+q+r) is in the range of 0.01-0.5; q/(k+l+q+r) is in the range of 0.1-0.6; and r/(k+l+q+r) is in the range of 0.1-0.3.
In another embodiment of the resist composition, the comonomer may include a (meth)acrylate monomer, maleic anhydride monomer, and norbornene monomer, and the formula of the photosensitive polymer may be one selected from the formulae: 
where R3 is a hydrogen atom or methyl; R4 is an acid-liable group; R5 and R6 are independently a hydrogen atom, hydroxyl, hydroxymethyl, 2-hydroxyethyloxycarbonyl, carboxyl, t-butoxycarbonyl, methoxycarbonyl, or substituted or unsubstituted alicyclic hydrocarbon having from 6 to 20 carbon atoms; k/(k+p+q+r) is in the range of 0.01-0.5; p/(k+p+q+r) is in the range of 0.1-0.6; q/(k+p+q+r) is in the range of 0.1-0.6; and r/(k+p+q+r) is in the range of 0.1-0.3, 
where R3 is a hydrogen atom or methyl; R4 is an acid-liable group; R5 and R6 are independently a hydrogen atom, hydroxyl, hydroxymethyl, 2-hydroxyethyloxycarbonyl, carboxyl, t-butoxycarbonyl, methoxycarbonyl, or substituted or unsubstituted alicyclic hydrocarbon having from 6 to 20 carbon atoms; l/(l+p+q+r) is in the range of 0.01-0.5; p/(l+p+q+r) is in the range of 0.1-0.6; q/(l+p+q+r) is in the range of 0.1-0.6; and r/(l+p+q+r) is in the range of 0.1-0.3, and 
where R3 is a hydrogen atom or methyl; R4 is an acid-liable group; R5 and R6 are independently a hydrogen atom, hydroxyl, hydroxymethyl, 2-hydroxyethyloxycarbonyl, carboxyl, t-butoxycarbonyl, methoxycarbonyl, or substituted or unsubstituted alicyclic hydrocarbon having from 6 to 20 carbon atoms; (k+l)/(k+l+p+q+r) is in the range of 0.01-0.5; p/(k+l+p+q+r) is in the range of 0.1-0.6; q/(k+l+p+q+r) is in the range of 0.1-0.6; and r/(k+l+p+q+r) is in the range of 0.1-0.3.
In another embodiment, the present invention provides a resist composition comprising a photosensitive polymer including at least one of the monomers having the respective formulae: 
where R7, R8, R9, R10, R11, R12, R13, R14, and R15 are independently a hydrogen atom or alkyl, and z is an integer from 1 to 6.
In the resist compositions according to the present invention, the photosensitive polymer has a weight average molecular weight of 3,000 to 100,000.
The amount of the photoacid generator (PAG) is in the range of 1 to 30% by weight based on the weight of the photosensitive polymer. It is preferable that the photoacid generator (PAG) comprises triarylsulfonium salts, diaryliodonium salts, sulfonates or a mixture of these materials. More preferably, the photoacid generator (PAG) comprises triphenylsulfonium triflate, triphenylsulfonium antimonate, diphenylionium triflate, diphenyliodonium antimonate, methoxydiphenyliodonium triflate, di-t-butyidiphenyliodonium triflate, 2,6-dinitrobenzyl sulfonates, pyrogallol tris(alkylsulfonates), N-hydroxysuccinimide triflate, norbornene-dicarboximide-triflate, triphenylsulfonium nonaflate, diphenyliodonium nonaflate, methoxydiphenyliodonium nonaflate, di-t-butyldiphenyliodonium nonaflate, N-hydroxysuccinimide nonaflate, norbornene-dicarboximide-nonaflate, triphenylsulfonium perfluorooctanesulfonate (PFOS), diphenyliodonium PFOS, methoxydiphenyliodonium PFOS, di-t-butyldiphenyliodonium triflate, N-hydroxysuccinimide PFOS, norbornene-dicarboximide PFOS, or a mixture of these compounds.
It is preferable that the resist composition further comprises an organic base. It is preferable that the amount of the organic base is in the range of 0.01 to 2.0% by weight based on the weight of the photosensitive polymer. The organic base preferably comprises a tertiary amine compound alone or a mixture of at least two tertiary amine compounds. More preferably, the organic base comprises triethylamine, triisobutylamine, triisooctylamine, triisodecylamine, diethanolamine, triethanolamine or a mixture of these compounds.
It is preferable that the resist composition further comprises a surfactant in an amount of 30 to 200 ppm.
It is preferable that the resist composition further comprises a dissolution inhibitor in an amount of 0.1 to 50% by weight based on the weight of the photosensitive polymer.
The photosensitive polymer, which constitutes the photoresist composition according to the present invention, includes a hydrophilic cyclic lactone in its backbone. Thus, the resist composition prepared from the photosensitive polymer has superior adhesiveness to the underlying material layer, excellent resistance to dry etching, and improved transmittance. When forming line patterns from the resist layer deposited with the resist composition according to the present invention, line edge roughness characteristic is improved. The dissolution contrast characteristic, which appears after developing, sharply increases, thereby enlarging the depth of focus (DOF) margin. The photosensitive polymer of the resist composition according to the present invention has a desirable glass transition temperature, so that the resist composition prepared with the photosensitive polymer exhibits superior lithography characteristics.